Imaging Techniques
Plain film X-ray: Plain film radiography is often used as
first-line imaging to demonstrate a lymphatic leak. Chest x-ray often
demonstrates a pleural effusion and abdominal x-ray may suggest the
presence of peritoneal fluid.
Ultrasound: Ultrasonography is particularly sensitive for
detecting the presence and quantity of fluid. Ultrasonography can
demonstrate dilation of intestinal loops, diffuse thickening of walls
and mesenteric edema. Sonographic evaluations are limited in the setting
of obesity or complex multiloculated ascites.
Computed Tomography (CT): CT can identify focal lymphatic
malformations, thoracic lymphangiectasia or lymphangiomatosis, but
distinguishing lymphatic fluid from non-lymphatic effusions is
difficult. Abdominal and pelvic CT scans obtained with oral and
intravenous contrast enhancement may demonstrate diffuse, nodular, small
bowel wall-thickening and edema.[4] Chylous ascites may demonstrate
a unique biphasic fat-fluid level when the patient to positioned lying
flat.[9]
Conventional Intranodal Lymphangiography: Percutaneous canulation
of groin lymph nodes followed by injection of an oil-based iodinated
contrast agent allows for imaging of the central conducting lymphatic
vessels with adequate characterization of patterns of lymphatic
flow.[10] Compared to historic use of pedal lymphangiography, direct
contrast injection into lymph nodes of the groin has a higher success
rate to produce informative diagnostic imaging of abdominal and thoracic
lymphatics. Although modern interventional practices have shortened
procedure time and decreased cumulative fluoroscopy exposure, anesthesia
is required for pediatric patients and should be discussed when
reviewing the risks and benefits of pursuing lymphangiography.
Conventional intranodal lymphangiography is contraindicated in patients
with a known right to left cardiac shunt given the potential stroke
risk.
Non-contrast Magnetic Resonance Lymphangiography: Static T2
weighted non-contrast MR lymphangiography has a high sensitivity and
specificity to demonstrate abnormal lymph vessels and abnormal draining
patterns in the peripheral lymphatic system.[11] Non-contrast MR
lymphangiography can image both central and peripheral lymphatic systems
but is a static image with no data to characterize lymphatic flow.
Magnetic resonance imaging (MRI) reduces ionizing radiation exposure but
may require sedation for prolonged studies.
Dynamic Contrast-Enhanced MR Lymphangiography (DCMRL): DCMRL is
the current imaging modality of choice to image the central lymphatic
system, identify lymphatic leaks and plan interventional or surgical
procedures.[10] However, the availability of DCMRL can vary
nationally and success of imaging can be operator dependent. The
technique has several advantages over conventional fluoroscopic
lymphangiography including that it is 3D, has good distal distribution
of contrast, and has good tissue contrast. Intranodal DCMRL (IN-DCMRL)
involves ultrasound guided groin lymph node access followed by injection
of a gadolinium contrast agent into the lymph node and then dynamic and
static contrast enhanced MRI imaging of the abdomen and thorax.[12,
13] This technique is good for imaging the central lymphatic system
including the cysterna chyli and thoracic duct (TD) and is the default
imaging modality for pulmonary lymphatic disorders that are often
supplied by fluid that originates from the TD (Figure 2a) .
IN-DCMRL allows for evaluation of the central lymphatic system prior to
interventions or surgery; however, the two main contributors to central
lymphatic flow, the liver and the mesentery, which play a key role in
several disease processes such as protein losing enteropathy (PLE) and
ascites, are not often imaged with IN-DCMRL. Recently, intrahepatic (IH)
and intramesenteric (IM) DCMRL allow imaging of these two important
lymphatic streams.[14, 15] Intrahepatic and intramesenteric DCMRLs
are the imaging modalities of choice for imaging abdominal lymphatic
abnormalities such as PLE and ascites and should be used in conjunction
with IN-DCMRL in cases with multicompartment lymphatic disorders to
better characterize the extent of the lymphatic abnormality and to plan
treatments (Figure 2b, 2c).